The disclosure relates to an adjustment apparatus for a hydrostatic piston machine, in particular a hydrostatic axial piston machine of swash-plate design or of inclined-axis design, and to a hydrostatic piston machine having an adjustment apparatus of this kind.
DE 10 2008 048 507 A1 discloses an adjustment apparatus of this kind for hydrostatic piston machines. Said adjustment apparatus has an actuating piston which can be moved between two end positions and which is adjoined by two opposite actuating chambers to which pressure medium can be supplied and from which pressure medium can be discharged. The supply and discharge of pressure medium is controlled by a regulating piston of a regulating valve. A regulating force, which is dependent on the position of the actuating piston, is applied to said regulating valve, said regulating force being directed against a control force which acts on the regulating piston and acting in the direction of an inoperative position of the actuating apparatus. In the inoperative position of the actuating apparatus, the regulating piston is arranged in its neutral position and the actuating piston is arranged in a position which is determined by the actuation of the regulating valve. In order to generate the regulating force, an actuating lever which is rotatably mounted on a bearing pin and is connected to the actuating piston is provided in the regulating valve in order to generate the regulating force. The magnitude of the regulating force is dependent on the angular position of the actuating lever. Furthermore, two limbs are rotatably mounted on the bearing pin. Said limbs are connected to one another by a tension spring in such a way that a deflection of one of the two limbs relative to the other limb leads to tensioning of the tension spring. A driver pin is arranged at one end of the actuating lever. In the event of a rotary movement of the actuating lever about the bearing pin, the driver pin rests against one of the limbs. When the spring is tensioned, the other limb is supported on an abutment which is provided on the regulating piston and applies the regulating force to said abutment. Two solenoids are provided for adjusting the regulating piston.
DE 100 63 525 B4 discloses a further embodiment of an adjustment apparatus. In this case, an actuating piston of which the movement is controlled by means of a regulating valve is likewise provided. A position of the actuating piston is fed back to the regulating piston of the regulating valve by a driver which is connected to the actuating piston. In this case, the regulating piston can likewise be moved to its regulating positions by means of two solenoids.
Documents DE 103 60 452 B3 and DE 10 2010 054 100 A1 each disclose an adjustment apparatus for a pivot cradle of an axial piston machine. In this case, a pivot angle of the pivot cradle can be pivoted by means of an actuating piston which acts on the pivot cradle. In order to increase the size of the pivot angle, pressure medium can be supplied to an actuating chamber which adjoins the actuating piston, wherein the actuating piston is moved in one direction. The actuating piston is indirectly acted on by a return spring (not shown in this document) in the opposite direction by means of the pivot cradle. A regulating valve is provided in order to supply pressure medium to and to discharge pressure medium from the actuating chamber. Said regulating valve is arranged coaxially in relation to the actuating piston in a common recess together with said actuating piston. In this case, a regulating piston of the regulating valve can be moved to first regulating positions in the direction of the actuating piston by means of a solenoid. A pressure medium connection between the actuating chamber and a low-pressure region of the axial piston machine is controlled in said first regulating positions. A spring force acts on the regulating piston by means of a mating spring, which is supported on the actuating piston, in the direction of second regulating positions, that is to say in a direction away from the actuating piston. The regulating piston controls a pressure medium connection between the actuating chamber and a high-pressure side of the axial piston machine in the second regulating positions. In order to apply the spring force to the regulating piston, said regulating piston projects out of the valve housing and into the actuating chamber by way of its end section, wherein a spring plate for the mating spring is arranged on the end section. The regulating piston is mechanically operatively connected to the actuating piston by the mating spring, this leading to the regulating piston controlling the pressure medium connection between the actuating chamber and the low-pressure side or the high-pressure side of the axial piston machine, depending on a pivot angle of the pivot cradle.
One disadvantage in the embodiments explained above is that, on account of hysteresis of the solenoids, said solenoids move the regulating piston differently when an identical control current is applied. This in turn leads to different adjustment of the actuating piston which in turn adjusts, for example, the pivot cradle at different pivot angles. Hysteresis of the solenoids can therefore lead to pivot angle hysteresis of the pivot cradle. In practice, a deviation in an actual pivot angle in relation to a desired setpoint pivot angle can be, for example, up to 6%.
In contrast, the disclosure is based on the object of providing an actuating apparatus for a hydrostatic piston machine and a hydrostatic piston machine having an adjustment apparatus of this kind, in which adjustment apparatus and hydrostatic piston machine pivot angle hysteresis is comparatively low. In this case, the pivot angle generally represents the deviation in the position of a reciprocating element, which determines the piston stroke, from a neutral position. In an axial piston machine of swash-plate design, the adjustable reciprocating element is the thrust plate which is then called the pivot cradle. In an axial piston machine of inclined-axis design, the adjustable reciprocating element is the cylinder drum. In a radial piston machine or a vane machine, the reciprocating element would be, for example, an eccentric ring.